When 'difftool' is called to compare a range of commits that modify
more than one file, it opens a separate instance of the diff tool for
each file that changed.
The new '--dir-diff' option copies all the modified files to a temporary
location and runs a directory diff on them in a single instance of the
Signed-off-by: Tim Henigan <firstname.lastname@example.org>
Signed-off-by: Junio C Hamano <email@example.com>